Process of and apparatus for heat pumping



Sept. 11, 1951 K. w. TACONIS PROCESS OF AND APPARATUS FOR HEAT PUMPING 2Sheeis-Shet 1 Filed March 2, 1950 bLT INVENTOR KRIJN W. TACONIS 'ATN P-1951 K. w. TAcoNls 2,567,454

PROCESS OF AND APPARATUS FOR HEAT PUMPING Filed March 2, 1950 2Sheets-Shea; 2

Patented Sept. 11, 1951 OFFICE PROCESS OF AND APPARATUS FOR HEAT PUMPINGKrijn Wijbren Taconis, Leiden, Netherlands Application March 2, 1950,Serial No. 147,205 In Sweden October 6, 1947 15 Claims.

This invention relates to a process of and apparatus for heat pumping inwhich a quantity of gas is periodically cooled and subsequently heated,either partly or entirely, to the original temperature, the expansion orcompression of a portion of the gas due to the cooling or heating of thewhole providing useful cooling or heating effects.

The invention relates more specifically to a process of and apparatus foproducing refrigeration by thermal expansion of a gas in an oblongvessel provided with one or more displacers that can be moved lengthwisein the vessel independently of each other and which together occupy thegreater part of the Vessel, such displacers when moved causing the gasto flow from one end of the vessel to the other Without any appreciabledifierence of the pressure at any instant throughout the vessel, andincluding means for efiecting regenerative heat exchange during the flowof gas from one portion to another of the vessel.

This application is a continuation-in-part of my copending applicationSerial No. 782,288 filed October 2'7, 1947.

A principal object of the present invention is to provide an improvedmethod of and apparatus for producing low-temperature refrigerationwhereby it is possible to obtain low and extremely low temperature witha high degree of emciency. Another principal object is to provide animproved method and apparatus for producing refrigeration by processinga gas through a cycle of compression and expansion events which avoidsthe difficulties attendant the use of an expansion engine or turbine byeffecting at least the expansion thermally.

A particular object is to provide a method and apparatus in which a gasis subjected to thermal compression as well as thermal expansion eventsso arranged that low temperature refrigeration is efiiciently producedfrom a supply of heat energy without the intermediate conversion of heatenergy to mechanical energy and the reconversion of mechanical energy toheat energy.

Further objects of the invention are to provide an improved method ofand apparatus for providing a net cooling effect in a body to berefrigerated by subjecting a confined body of gas to a cycle ofalternate heating and cooling in a manner which produces a quantity ofrefrigeration by the secondary cooling of a portion of such gas in heatexchange with the body to be refrigerated, which quantity is a large 2r7 portion of the product of the temperature change and the differenceof the specific heats of the gas at constant pressure'and at constantvolume.

In such cycles the gas may be compressed mechanically, for example, by acylinder fitted with a piston in which by asingle stroke the gas isgiven the required pressure and, if desired, .a low pressure reservoirmay be employed to reduce pressure fluctuations. It is also possible touse a high-speed multi-stroke compressor, or a number of compressors andpressure reservoirs containing gases with increasing pressures.

The invention particularly relates to a very economical expedient .forcompressing the low pressure gas to the required higher pressure in theprocess and apparatus of the present invention. To this end the gas iscompressed by a caloric compressor, which may 'be efiectively combinedwith the cold generating portion of the apparatus so that a very simplelow-temperature refrigerating machine is obtained with a high economicyield.

A caloric compressor is one :in which heat is imparted to a body of gasto be compressed, which heating causes the gas pressure to rise so thata portion of the heated gas may be delivered at higher pressure. Littleif any mechanical work is involved in a caloric or thermal compressor.Such compressors have been previously proposed (see, for example, UnitedStates Patent No. 2,157,229 of V. Bush).

These and other objects and advantages of the invention will becomeapparent from the following description and the accompanying drawings,in which:

Fig. 1 is a diagrammatic view of an embodiment of the invention in whichthe gas is mechanically compressed;

Figs. 2-0. and 2-2) are diagrammatic views 1illus trating the principleof operation of a thermal compressor;

Figs. 3-a, 3-2), and 3-c are three diagrammatic sectional views of apreferred embodiment of the invention for carrying out the process ofproducing low-temperature refrigeration, the

three views illustrating three different stages of the operating cycle;

Fig. 4 is a fragmentary diagrammatic sectional view of a chamber havingtwo gas displa'cers therein, the lower of which has portions ofdifferent diameter to provide the refrigeration at several steps;

Fig. 5 is a similar view of another alternative construction in whichthe lower Tdisplacer is provided with concentric annular steps;

Fig. 6 is a similar view illustrating a modification employing amultiple number of displacers, the lower of which are arranged to blifted successively;

Figs. '7 and 8 are respectively cross-sectional and fragmentarylongitudinal sectional views of a vessel with displacers therein andmeans between the displacer and vessel wall for increasing th capacityof the wall for regenerator action; and

Fig. 9 is a diagrammatic view of another embodiment of the apparatus ofFigs. 4 to 6 in which the regenerator is external to the wall of thevessel.

With reference to the accompanying drawing, a refrigerating machineemploying a mechanical compressor, and a thermal expander with a movabledisplacer within an elongated vessel, is illustrated, in Fig. 1. Forsimplicity only one displacer is employed in the vessel and the innerwall of the vessel acts as a regenerator.

An oblong, for example cylindrical, vessel which may be externallyinsulated, is indicated at II and this contains a displacer body I2which although closely fitting the'inner wall of the cylinder hassubstantial clearance so that it is capable of being moved freelylongitudinally. The displacer is moved by suitable means, for example,by an operating rod I3 or the like, movable through the end of thevessel II. At the top, vessel I I is connected toa tank or gas reservoirlfi'through a conduit I4 controlled by a valve I5, and to a'highpressure gas reservoir I9 by a conduit I'I controlled by valve I8.Reservoirs I6 and I9 are connected by a conduit I I] having interposedtherein a compressor C for pumping gas from tank I6 to reservoir I9 at arate required for keeping the pressure in tank I6 at a constant lowvalue. The inner walls of vessel II are of a material, and may be soconstructed, that such walls in cooperation with the walls of thedisplacer I2 will act as heat accumulators or regenerators.Alternatively the displacer may be closely fitted to smooth inner wallsof the vessel I I and passages filled with regenerative material mayconnect the upper and lower ends of the vessel II. 1

With the aid of the apparatus illustrated in Fig. 1, one modification ofthe process according to the invention is realized as follows: aquantity of gas is admitted from reservoir I9, in which the pressure isat a high value P, through conduit I'I into the top of vessel II byopening valve I8. The displacer I2 is in its lowest position as shown.It is assumed that the apparatus is in thermal equilibrium condition, inwhich the temperature at the top of the vessel I I is relatively high,hereafter designated Tm, while the temperature at the bottom is low andis designated Tb. The wall of the vessel II acting as a regeneratorinsures that the gas being displaced from the top to the bottom iscooled to temperature Tb and heated again to temperature Tm when passedfrom the bottom to the top of vessel I. For the purpose of anillustrative example, temperature Tm may be taken to be 300 K. andtemperature Tb to be 100 K., the pressure P amounting to approximately10 atmospheres. When displacer I2 is lifted, the ga in chamber II passesbetween the displacer and the walls and absorbs so much cold that onreaching the bottom it has assumed the temperature Tb.

Thus inlifting displacer I2 an ever increasing portion of the gas iscooled from temperature Tm to temperature Tb. Since this occur under 4conditions in which the total volume of the gas remains constant, thegas pressure is gradually reduced from the original value P to a lowvalue p, which final pressure is attained upon the total amount of gasreaching the bottom portion of the vessel II.

The pressures P and p are more or less proportionate to the temperaturesTm and Tb. When the gas is displaced from the top to the bottom of thevessel, the pressure consequently decreases and refrigeration due toexpansion is produced preferably exclusively at the top and the bottomof vessel II, when of course the gas volume of the regenerator space isleft out of consideration. Such volume is the volume of gas present inthe space between the displacer I2 and the wall of vessel II, whichspace is small in respect to the other volumes concerned.

The refrigeration produced at the top of the vessel II is removed bysuitable means such as cooling water that may be flowed in heat exchangewith the top of vessel II to keep it at the constant temperature Tm.Such quantity of refrigeration generally cannot be effectively used. Therefrigeration produced at the bottom of the vessel II at a temperatureTb, however, may be applied usefully to cool a substance to berefrigerated. For example, a fluid to be refrigerated may be flowed inheat exchange with the bottom of the vessel I I.

Thereupon valve I5 is opened and the displacer I2 is moved downward. Thecold gas now flows upward at the low pressure p and during such flowthrough the regenerator walls the gas is heated to the temperature Tm.The tank I6 provides a space for the gas to flow into at a substantiallyconstant low pressure p since provision is made for the pressure in thevessel I6 to be maintained at th value 7). During this stage of theprocess the regenerator gives up as much heat to the gas as it absorbedtherefrom in the first step. Finally the gas may be compressed by meansof compressor C from the low pressure p to the high pressure P andpassed to the high pressure reservoir I9. Valve I5 is now closed andvalve I8 is opened so that a new quantity of gas at a high pressure canbe admitted into vessel I I, after which valve I8 is again closed andthe process is repeated.

Assuming an ideal gas, that Cp is the specific heat of such gas atconstant pressure per mole, Cv is the specific heat at constant volumeper mole, and Tm and Tb are the original and final temperatures, in thefirst step of the process the regenerator absorbs per 1 mole of the gasan amount of heat equivalent to CpX (Tm-Tb). The condition that theregenerator is cooled at constant pressure is closely approximated ifthe pressure of the gas remains practically unchanged when a certainpart by volume of the gas passes through the regenerator. Actually sincethe cooling of the gas is effected in such a manner that the totalvolume of the gas in vessel II remains constant, the total quantity ofheat withdrawn from the gas amounts only to The difference between thesetwo quantities, i. e. C72Cv (TmTb) therefore constitutes the amount ofheat to be supplied to the gas at both the top and bottom of vessel II,in other words, the total quantity of cold produced per mole of the gasunder ideal conditions. In the second step of the process, the quantityof cold absorbed by the regenerator at constant pressure p is equivalentto. Op- (CZ-Zm: Tb).= so that: each. time the amount of cold. absorbedby the. re enerator inthesecond step equals thequantity of; cold.delivered. in the first; step and. during the. second step. of theprocess no; more. cold. or heat is produced.

The cooling of: the. topof the vessel H by cool.- i-ng water precludes.heating of the gas in the. top of vessel H due. to compression.Furthermore, compressor C. has its. own cooling arrangement so. that.the; temperature of. the; gas in. the; pressure vessel; |9 will be.about; equal to; the temperature of the surrounding atmosphere or of thecooling water:

The operation: of; a. caloric compressor, which according. to the.invention. is: advantageously combined with the above. described:thermal ex.- pansion device, is diagrammatically illustrated in Figs.2-0. and 27b; The thermal. compressor comprises a. chamber or. cylinder2.0 in which a displacer '2'! is movable up and down by a; driving rod22. Inlet and outlet conduits 23- audl l con.- nect to the bottom ofthe: cylinder Zll andiare. controlled by valves 25. and 26 respectively;'Ilhebottom of the cylinder 20 may be maintained at. a temperature I'm,for example, by cooling coils not shown through which cooling water ispassed or similar to cooling passage I3- in the aforementioned PatentNo. 2,157,229.. Heat is supplied to the top of the; cylinder 2t; insuch. a. manner, for example, by a gas burner not. shown, that aconstant temperature Tit. prevails there. For the sake of uniformitywithv the previously assumed. ex:- am-ple, the temperature Tmmay betaken to be 390 K. while the temperature 'It may have a I value of about909 K.

In- Fig. '2--a. the displacer Zxl in. the. cylinder. 20. has assumed thetop position and gas: has been admitted through the valve 25 and conduit23 into the bottom of the cylinder. This gas has a pressure which wouldamount.- to 1 atmosphere if the gas is supplied. directly from the:atmosphere. Although displacer 2f closely fits. the: wall of cylinder20, it iscapable of moving'freelytherein with enough clearance so that.the. gas may easily pass between the displacer 2 I. and the. wall ofvessel 2|] from one end to the other. Displacer ZI- is now moveddownwardly, which causes part of the gas to flow upwardintotheheatedltop. of the cylinder 28-. expander, the wall of cylinder20. acts as, a generator and insures that the cold gas passing upward isheated to the; temperature It. Since. the total volume of the; gasduring this step: remains constant and the temperature of. at: leastpart of the gas rises, the pressure of. the gas: in.- creases. The gashaving attained: the desired higher pressure P may be discharged. viavalve 26 and conduit 24 from the: bottom of the: cylinder. It should benoticed that the gas, passing through the line 2-4 has the relativelylower temperature Tm. The further dis-placer H is moved downward, moregas is forced out through line 24' at the constant pressure P. Thisprocess is: continued until displacer 2-1. has reached its: lowestposition, as illustrated by Fig. 2b.

Valve 26 is then closedand displacer 21 lifted again, which reduces. thegas pressure to the value p. This value having been attained, the valve2'5 may be opened toadmit gas through line 23 duringthe period throughwhich the displacer H is moved further to its highest position;thereupon the aboveoutlined steps may be repeated.

In accordance with the preferred embodiment of the invention, bycombining such a caloric As in the case of the thermal 1 compressor withthe thermal expansion. apa paratus, a cooling machine obtained havin a.high economic yield. The work. required to bring. the gas from the lowerpressure p to the high pressure P in the case of Fig; 1. is supplied bya mechanical energy consuming; compressor. By transforming mechanicalenergy into com.- pression work, a fairly high yield; is obtained, viz.,approximately 60%. However, this is: not the case when the energycontainedin fuel. is converted in the customary manner into themechanical used by the compressor, for: example, from. heat energy toelectric energy to mechanical energy. such conversion. at best usuallyresults in a. yield of. less than 3.0%. By converting heat energy offuel. directly into compression energy and. omitting.- the intermediateconversions, an improvement in the yield bya factor of approximately 5may be ob.- tained; under certain. conditions. Even if the yield of the.cold generating portion. of the: apparatus is not particularly high, acombination of such apparatus with. the caloric; compressor may resultin very high economic yield ofirefrigeration. as compared with that ofthe known refrigeration machines.

The caloric compressor: described above may be substituted. directly forthe. compressor II in Fig. 1, however according to the invention thecaloric compressor and cold generating apparatus are further combinedinto avery simple eflicient refrigerating machine which will. now bedescribed in detail with reference. to Figs; 3'-a, 3-b, and. 3-0.

An oblong or cylindrical vessel 30 is provided with two. displacers 3;!and 32 disposed therein, each being capable of being independently orsimultaneously moved longitudinally in the vessel 31!. They maybe moved,for example; by driving rods 33 and 34, the rod 34 being secured to theupper end of displ'acer- 3.2 and. passing through an axial? passagethrough the displacer 3 The driving rod 33 for the displacer 3i may beatube surrounding the driving rod 34-. The driving rodsare secured tosuitable lifting elements not shown in the interests of clearness of thedrawing, for example, a lifting mechanism for a driving rod of a singledisplaceris shown in the aforementioned United States Patent No.2,157,229. the displacers and the wall of the vessel to allow the gas topass from one end to the other and provide regenerator action along thewalls. At the top of vessel 30 heating means indicated as a heating coil35 is provided to maintain the temperature there at the value Tz'z'(which. may, according to the. example, be about. 900 K). Atapproximately the middle of the vessel 30 there, is provided. a coolingcoil, for. example, a passage 35' for cooling. water which surrounds thevessel to, maintain the temperature. in, the middle zone substantiallyconstant, for example, about300 K. Thebottom-of the, vessel ismaintained at the. low. temperature Tb. which may, for example, be andvwhich, temperature is maintained. by a. heat exchange. coil- 31 carryinga fluid to be. cooled. When theapparatus is inoperation and in astateofthermaLequil-ibrium, the temperatures prevailing atv the top, themiddle,and the: bottom zones are: therefore respectively 'I-t, Tm, and Th.Those parts of the vessel wall lying between the top. and the middle andbetween the middle; and bottom zones act. as regenerators.v The combinedlength of the dis.-

Sufiicient space may be left between placer-s is less than the length ofthe chamber 30 by approximately or less.

In the first position, as shown in Fig. 3a, both displacers are as closeto the bottom of the vessel as possible, so that substantially all thegas is at the top, the height of the gas column at the top being denotedby the double-headed arrow a. The displacers 3| and 32 are then liftedtogether over a distance b as denoted by the space between the arrows inFig. 3-b. The distance b is a fraction of distance a which is dependentupon the temperature ratios employed and for the example indicated, thisdistance b will amount to approximately a. Part of the gas is displaceddownwardly along the regenerative walls and is cooled, causing thepressure to drop from P to p. In passing downward, the gas transfersheat to the regenerator, refrigeration being simultaneously produced atthe bottom and the top of the vessel 30 at the respective temperaturesTb and Ti. In the next step of the process, displacer 3| is lifted whiledisplacer 32 is moved downward again in such a manner as to cause thegas portion at the bottom of the vessel 30 to be forced upward to themiddle zone, whereby it is heated to temperature Tm, and the gas portionin the upper zone to be forced down into the middle zone and thus cooledto temperature Tm. This step is conducted so that the mean temperatureof the total active gas remains constant and the pressure remainsconstant at p. The end result of this step is illustrated in Fig. 23-0.In the last stage of the process, displacer 3| is moved downward so thatall the active gas passes from the middle zone to the top zone of vessel30 and is heated from the temperature Tm to the temperature Tt. Sincethe total volume occupied by the gas remains constant, the pressurerises again to the original value P.

It may be calculated that the production of refrigeration per mole ofthe gas at the top of vessel 30 at the temperature level of 900 K.amounts to approximately 1100 calories and the production ofrefrigeration at the bottom at a temperature level of 100 K. amountsapproximately to 100 calories. Due to the compression in the last stageof the process, 900 calories of heat are developed at the top of thevessel at the temperature level of 900 K. and 300 calories are producedin the middle zone of the vessel at the temperature level of 300 K.Consequently a total of 200 calories per mole must be added to the gasat a temperature of 900 K., and 100 calories of heat, which correspondsto the refrigeration production at 100 K., must be added at the bottomof the vessel. The amount of heat to be discharged to the cooling waterat 300 K. is therefore 300 calories.

The above-described cycle may be termed a modified three-step cycle andit will be seen to be a great improvement over a straight threestepcycle in which the distance b is 100% of distance a. Thus if thedisplacers were simply shifted back and forth in the chamber, no usefulnet effect would result because the expansion due to pressure drop whenthe gas was put into the cold end zone would be balanced by thecompression due to the equal pressure increase when the gas was shiftedinto the hot end zone. If, however, the displacers are moved in astraight three-step cycle, starting with the gas all in the hot zone; onthe first step the displacers lift all the way so that b equals a andall the gas moves into the cold zone, the pressure drop through amaximum range and refrigeration due to expansion is developed in thegas. On the second stroke or step only the lower displacer is loweredand all the gas is displaced to the middle zone. The gas is warmed tointermediate temperature, pressure rises to an intermediate value, andthe later portions of the gas to leave the cold end zone are partlyrecompressed before they leave this zone. Such partial recompressiondestroys part of the refrigeration at the cold end, so that only a partis recoverable for usefully cooling a fluid in heat exchange with thecold end. The third stroke drops the upper displacer and returns all thegas to the hot zone so that the pressure rises to the maximum. That heatof compression developed in the later portions of gas to leave themiddle zone is removed by heat exchange to the cooling water.

The modified three-step cycle according to the invention avoids thedestruction of useful refrigeration at the cold end by removing the gasin the cold end under a constant pressure. The first stroke raises thedisplacers 3| and 32 only a selected part b of the distance a such thatthe volume of gas transferred to the cold zone is a selected fraction ofthe total volume of gas that was in the hot zone. This fraction may befrom 15 to 44% and for the specific examples of temperatures hereinsuggested, is preferably about 26%. The pressure will drop only to thepressure (p) corresponding to the pressure when all the gas is in theintermediate zone because part of the gas is still at high temperature.For the second stroke the displacers 3| and 32 are moved apartpreferably in timed relation such that the average temperature of allthe gas remains constant and the pressure does not change. The gasportion in the cold zone is heated at constant pressure as it istransferred to the middle zone and the gas portion in the hot zone iscooled at constant pressure as it is transferred to the middle zone.Thus, although the refrigeration produced in the cold zone is not asgreat as in the straight three-step cycle, none of the refrigeration isdestroyed. In the third stroke the lower displacer 32 remains at thebottom and the upper displacer 3| is dropped to shift all the gas fromthe middle zone to the hot zone. It will also be seen that the smallerpressure change greatly improves conditions in the hot zone because lessexpansion occurs in the hot zone gas and its actual temperature remainsmore nearly constant. Ideally all the heat added at the hot zone shouldbe at the high temperature (900 K.) and with a smaller pressure changemore of the heat is added at the high temperature and less is added atlower temperatures.

When suitable allowance is made for thermodynamic losses including thedeviation of the gas from the ideal, that the compressions andexpansions follow adiabatic laws, allowance for dead gas holding spacessuch as clearance spaces and regenerator space, allowance for gas flowfriction losses and heat exchange inefficiencies; it is found that thestraight three-step cycle is so affected by these losses that the usefulrefrigeration obtained is too small to be economically useful, while onthe other hand the modified three-step cycle according to the preferredembodiment of the invention provides an unexpectedly large amount ofuseful refrigeration for a given input of heat energy in an economicalsize of apparatus.

The following sets forth a specific example of the effect of selectingthe ratio 12/11 of lift for step 1. It is assumed in the following thatthe *9 mean temperatures at the hot middle and cold ,zones aremaintained at 700 K., 300 K., and 100 K., and that suitable allowancesfor losses are the same in each instance and the gas is monatomic Belowabout lift and above 44% lift the results become uneconomical for theproduction of refrigeration at the low temperature of 100 K. Thistemperature is particularly useful for liquefaction of air undermoderate pressures. Still lower temperatures for liquefaction of other"permanent gases are readily attainable.

Sometimes it may be desired to produce part Of the refrigeration atdifferent temperature levels higher than the lowest temperatureproduced, for example, for the cooling as well as the liquefaction ofair. In such a case, the total quantity of refrigeration may be producedat the various temperatures required. To this end the shape of thevessel and the displacer may be modified, for example, as shown in Fig;4, where the lower displacer I32 may have successively smaller diametralsteps toward its bottom end and the vessel I39 is shaped correspondinglyat its lower end. This modified structure provides the result that therefrigeration is produced not only at the bottom but also at each of theshoulders I38 and I39 of the lower end of the chamber. The steps are tobe of substantially equal height and regenerative action is providedalong the walls at each step.

Another modification for accomplishing similar results isdiagrammatically illustrated in Fig. 5, wherein the steps at the bottomare in the form of concentric annular projections from the bottom of thevessel 230, in which are fitted corresponding annular portions 238, 239of the displacer 232. Upon upward movement of the displacer the gas willfiow substantially radially inward toward the center and the lowesttemperature refrigeration will be produced in the central depression.

A similar efiect may also be achieved by a modification illustrated inFig. 6 in which the vessel .330 is cylindrical and a plurality of equaldiameter displacers therein are employed. These displacers are moved sothat the lower displacers are moved through shorter distances than theupper displacers. Five displacers are shown for example, there being oneupper displacer 33I and a group of four lower displacers 3.32-A, 332-3,332-C, and 332-D, all of which may be moved by the same operating rod333 by providing successively larger clearance spaces betweenprojections 333-3, 333-0, and 333-D on the rod and a portion of thedisplacer engaged by the projection. The displacer 332-A may be directlyconnected to the operating rod 333, while the clearance space betweenprojection 333-13 and displacer 332-13 is a small amount and thosebetween projections 333-C, 333-D and displacers 332-0, 332-D arerespectively larger. Thus when the rod 333 is lifted, the displacer332-A is moved throughout the full lift distance and the lower displacerportions are successively lifted over increasingly smaller distances,whereby refrigeration at several temperature levels may be developed inthe several spaces created between the several members of thelowerdisplacer group. The energy-supplying means in the form of a suitableheating means, for example a gas burner, may be disposed externally atthe top of the vessel 330. The coolingcoil for cooling water is disposedexternally around the vessel 339 in the region between displacers 33land 332-A. The fluid to be cooled may be passed in thermal contact; withthe vessel 330 in the region from below displacer portion 332-A towardthe bottom, and if such fluid is flowed in the downward direction itwill be cooled gradually to the lowest temperature. The embodimentillustrated in Fig. 6 has an additional advantage in that the distancetraversed by the displacers in respect to the vessel will .be reduced.This fact is of importance because an increase of such distance wouldinvolve an increase in the temperature gradient between opposite pointsof the displacer and the wall of the vessel, which. would result inincreased thermo-dynamic losses.

Such losses can also be reduced by fitting between the inner wall of thevessel 30 and the outer wall of a displacer 32, as shown in Figs. '7 and.8, one or more coiled bands, as diagrammatically indicated at 40. Suchband is preferably helically coiled and provided with several turnsbetween the wall, thus the displacer retains its freedom of movement,the heat capacity of the wall acting as .a regenerator is increased andthe heat exchange between the wall and the vessel is reduced.

The losses caused by the difference in temperature of momentarilyopposed parts of the displacer and the wall of the vessel may also ,bereduced by providing between them. a movable partition or wall capableof being shifted along or half the distance covered by the displacer, orthe perspective part of the displacer. If desired, there may be anarrangement of more than one such partition. The valves, displacers, andthe like employed in the various embodiments described herein arepreferably operated by suitable mechanism so as to be movedautomatically in timedsequence.

In the embodiments of the invention described above, the vessel wallswere described as arranged to act as regenerators as the gas flowedbetween the wall of the vessel and the wall of the displacer. It is also-possible, and in some practical cases preferable, to cause the gas topass through passages in or outside the inner wall of the vessel orregenerative passages through the displacers.

An embodiment employing regenerators in a passage associated with thewall of the vessel is illustrated diagrammaticallyin Fig. 9. In Fig. 9 aregenerator passage 50 filled with suitable ,regenerator mass 5!, suchfor example as crosscoiled wire, punched metal pieces, et cetera, is

connected at both ends to the ends of the vessel 430 by passages 52 and53, and an intermediate connection 54 is provided between theregenerator 50 and the intermediate region of the vessel 430. In Fig. 9the heating means for the hot end is indicated by a gas burner 55 thecoolingcoil carrying cooling water is indicated at 56, anda coil for thesubstance to be refrigerated is indicated at 51 wound around the coldend of the vessel 430. To provide free communication to the middleconnection between the vessel and regenerator the inner end of thedisplacer 43I is provided. with a somewhatreduced diameter at 58. If itis de- 1 1 sired that the regenerator passages shall be within thedisplacers, such regenerator passages may extend from one end to theother of the displacers. In such modifications, with regeneratorsassociated with the wall of the vessel or within the displacers, thedisplacers need not be fitted gastightly against the inner wall of thevessel, however a closer fit is required so that the flow resistance ofthe gas along the walls is sufficiently greater in respect to the flowresistance through the regenerators that most of the gas will passthrough the regenerators.

The gas which is employed may be any gas which is not liquefied at thelowest temperature produced. When very low temperature refrigeration isbeing produced, a gas such as hydrogen or helium is preferable. Specificconditions to be met will indicate whether monatomic or diatomic gas ispreferable. In general the size of the apparatus is reduced by chargingthe chamber initially with the gas under a high pressure, for example,atmospheres. When hydrogen or helium is used, substantially higherinitial pressures may be used because such gases are not liquefiable attemperatures as low as 100 K. and substantially lower.

The portion of the apparatus that serves as a heat accumulator orregenerator may be regarded as a body or mass, the temperature of whichdecreases gradually from one end to the other. Such a body should have ahigh heat capacity in relation to the capacity of the gas, while theother parts of the apparatus should have a low heat capacity to avoidsecondary losses. When the cylinder wall is constructed to serve as aheat accumulator it should have a high heat capacity, and the'displacersthen should have low heat capacity. When the displacers are employed asheat accumulators, they should have a high heat capacity and the wall ofthe vessel should have low heat capacity. In both cases the heatconductivity of the wall as well as of the displacers should berelatively low in the longitudinal direction. The length of the portionof the vessel not occupied by the displacers should be preferably smallin proportion to the length of the vessel. Otherwise the difference intemperature in the spaces available for the gas when the displac'ers aremoved would be so large that undesirable heat exchanges may take place.

That the degree of lift or volume of gas admitted to the cold zoneshould be less than 50% of the original gas space or of the total volumeof active gas, is seen to be due to the greatly increased density of thegas at the lower temperature. Thus if the lift is only 26%, about 0.7 ofthe total weight of gas will be in the 100 K. zone and about 0.3 of thetotal weight of gas will remain in the -700 K. zone. A lift of about 12%still results in about one-half the gas by weight flowing into the coldzone. In general, the smaller lifts appear to be more useful with largertemperature differences and vice versa and the useful range of lifts isfound to lie between about 12% and under 50%. As hereinbefore indicated;the high temperature, for example 600 K. to 900 K., will be selectedpreferably according to the materials of construction, the temperatureefllciently produced by the specific heat source employed, andconsiderations of efficient heat exchange; the intermediate temperatureis preferably a value providing efficient heat exchange to a convenientcooling medium such as water, for example, of the order of 300 K.; andthe low temperature is selected to provide efficient heat exchange witha fluid to be refrigerated, such as a gas to be liquefied. Obviously,heat insulation and apparatus constructions are to be employed with aview to minimizing adverse heat leakages.

The process and apparatus according to the invention is useful broadlyas a heat pump in which heat energy is supplied or rejected at onetemperature, is absorbed or rejected at another temperature, and isrejected or supplied at a different temperature. For refrigeration, heatat low temperature absorbed from a substance to be refrigerated isrejected to a cooling medium at a higher temperature as a result of therejection to the cooling medium of heat supplied at high temperature;for heating, expensive high-temperature heat energy may effectabstraction of additional heat from a low-cost low-temperature source sothat more heat at intermediate temperature may be gained; and by areversal of the cycle, heat may be absorbed at intermediate temperatureand rejected to a warmer cooling medium and a colder refrigerant. Theworking fluid employed is preferably a gas deviating as little aspossible from the properties of an ideal gas. Air or nitrogen may beused if the cold zone temperatures are not extremely low and fortemperatures in the range of the boiling points of oxygen and nitrogen,hydrogen or helium are preferred.

It will be understood that modifications of the process and apparatusaccordingto the invention may be made without departing from theessentials of the invention and that subject matter in the abovedescription and shown in the accompanying drawings shall be interpretedas illustrative and not in a limiting sense.

What is claimed is:

1. A process for producing refrigeration which comprises providing aconfined body of gas under pressure and at an initial high temperature;cooling at least a portion of the gas to a relatively low temperature atconstant total volume to reduce the pressure, thereby inducingrefrigeration in said portion and in the remainder; heating said portionwhile cooling said remainder, both at constant pressure to anintermediate temperature; heating said gas from the intermediatetemperature to said initial high temperature; and abstracting for use asubstantial amount of the refrigeration induced in said portion.

2. A process for producing refrigeration according to claim 1, in whichthe amount'by volume of said portion with respect to the total activevolume of the gas is selected to be between 10 to 50% according to thetemperature levels.

3. A process for producing refrigeration according to claim 1 in whichthe initial high temperature is 700 K. to 900 K., the intermediatetemperature is about 300 K., the relatively low temperature is about K.,and the amount by volume of said portion with respect to the totalactive volume of the gas is of the order of 26%.

4. A process for producing refrigeration which comprises confining abody of gas in a closed system having hot, intermediate, and cold zones,the gas being initially under a desired pressure and high temperature insaid hot zone; passing the gas from the hot zone directly to the coldzone while cooling it to a relatively low temperature at constant totalvolume, to reduce the pressure and thereby induce refrigeration therein;passing the gas from the cold zone to said intermediate zone whileheating it to an intermediate temperature, thereby increasing thepressure and inducing heat of compression therein; removing heat fromsaid intermediate zone to maintain the temperature acetate thereinsubstantially constant; passing the gas from the intermediate to the hotzone while heating it to said high temperature; supplying heat to thehot zone to maintain the temperature therein substantially constant;-andabstracting for use a substantial amount of the refrigeration induced inthe cold zone.

5. A process'for heat pumping which comprises confining a bodyof gas ina closed system having hot, intermediate, and cold zones, the gas beinginitially at a desired pressure and high temperature in said hot zone;passing at least a portion of the gas from the hot zone to the cold zonewhile cooling it to a relatively low temperature at constant totalvolume to reduce the pressure and induce refrigeration in said portionat low temperature and in the remainder at high temperature; passingsaid portion while heating it and said remainder while cooling it bothto said intermediate zone and to an intermediate temperature; passingthe gas from the intermediate zone to the hot zone while heating it fromintermediate to high temperature; and cyclically repeating such stepswhile removing heat from said intermediate zone at the intermediatetemperature and supplying heat to the hot and cold zones at theirrespective temperatures.

6. A process for heat pumping according to claim in which the heatingand cooling of the gas during the passages between zones is effectedregeneratively by heat exchange with heat storing material.

7. A process for heat pumping according to claim 5 in which the amountby volume of said portion of the gas with respect to the total activevolume of the gas is selected to be between to 50%.

8. An apparatus for heat pumping comprising a closed chamber having ahot Zone at one end, a cold zone at the opposite end, and anintermediate zone of intermediate temperature; gas displacing meansoccupying a major part of the space of said chamber, said displacingmeans comprising at least two displacers; a charge of gas in saidchamber under pressure; passage means interconnecting said zones forpassing gas between the zones without appreciable pressure difference;operating means for cyclically moving said displacers to displacesubstantially all the gas to the hot zone, to displace gas from the hotzone directly to the cold zone, to displace the gas all to theintermediate zone, and to displace all the gas from the intermediatezone to the hot zone; and means for removing heat from the intermediatezone while supplying heat to the hot and cold zones.

9. An apparatus for heat pumping according to claim 8 which includesregenerator means in said passages between said zones.

10. An apparatus for heat pumping according to claim 8 in which saidpassages between zones are provided by clearance space between the wallof the displacing means and the wall of the chamber and in which one ofsaid walls is constructed to provide regenerative heat storage.

11. An apparatus for heat pumping according to claim 8 in which saidpassage means is associated with the wall of said chamber and isconstructed to provide regenerative heat storage.

12. An apparatus for heat pumping comprising a closed chamber having ahot zone at one end, cold zones at the opposite end, and an intermediatezone of intermediate temperature; gas displacing means occupying a majorpart of the ill) 14 space of said chamber, said displacing meanscomprises first and second displacer .units mov= able respectivelyintothe hotiand colder portions of the chamb'enisa'id colder portion of the:cham-' ber and 'said second displacer unit being coop=eraitively'constructed to divide the colder portion into a pluralityoficol'd zones interconnected by passages; a charge of gas in saidchamber under pressure; passage means interconnecting said zones :forpassing .gas between the zones without appreciable pressure difference;operating means for cyclically moving said displacing means to displacegas from the hot zone directly to the cold zones, to displace the gasall to the intermediate zone, and to displace all the gas from theintermediate zone to the hot zone; and means for removing heat from theintermediate zone while supplying heat to the hot and cold zones.

13. An apparatus for producing refrigeration directly from heat energywhich comprises a closed chamber having a charge of gas under pressuretherein, hot and cold zones adjacent opposite ends, and an intermediatezone; two gas displacers within said chamber which together occupy amajor part of the volume of the chamber, the first displacer beingmovable into said hot zone and the second displacer being movable intothe cold zone, the displacers being also movable toward and away fromcontact with each other; passage means interconnecting said zonesproviding for the flow of gas without substantial pressure differencebetween the zones when displaced by the displacers; means for removingheat from the intermediate zone while supplying heat to the hot and coldzones; and operating means for cyclically moving the displacersconstructed and arranged to move both displacers simultaneously from aposition nearest the cold end to a position part way toward the hot end,then move the displacers apart, the first into the hot zone and thesecond into the cold zone, and finally move the first displacer out ofthe hot zone and into contact with the second displacer.

14. A process for producing refrigeration directly from heat energywhich comprises confining a body of gas in a closed system; cyclicallycooling a portion of such gas from a high temperature to a lowtemperature, the total gas volume remaining substantially constant andthe pressure in the system dropping; heating said portion of gas atsubstantially constant pressure to an intermediate temperature, theremainder of the gas being simultaneously cooled from said hightemperature to said intermediate temperature to keep the pressure in thesystem substantially constant; recombining said remainder with saidportion; heating the combined gas from the intermediate temperature tosaid high temperature, the total gas volume being maintainedsubstantially constant and the pressure rising to the original highervalue; and removing heat from the gas when at the intermediatetemperature while supplying heat to the gas respectively at the hightemperature and the low temperature.

15. A process for heat pumping which comprises confining a body of gasin a closed system having warm and cold end zones and an intermediatezone, the gas being initially in the intermediate zone at anintermediate temperature; displacing the gas to one of said end zoneswhile effecting a heat exchange to change its temperature to thetemperature of such end zone; displacing at least a portion of said gasdirectly to the other end zone while effecting heat xchange to changeits temperature to that of said other end zone; displacing the gas fromboth end zones 2597,45 1 K 15 g 18 to said intermediate zone to returnall said gas to the intermediate zone under substantially con-REFERENCES CITED stant pressure while effecting heat exchange to changethe gas temperatures to the temper- The following references are ofrecord in the file of this patent:

ature of the intermediate zone; and cyclically re- 5 peating such stepswhile effecting heat exchanges UNITED STATES PATENTS with said zones tomaintain their respective tem- N e ame Date peratures. 1,275,507Vuilleumier Aug. 13, 1918 2,127,286 Bush Aug. 16, 1938 KRIJN WIJBRENTACONIS. 10 2,175,376 Bush et a1. Oct. 10, 1939

